1. Field of the Invention
The invention pertains to a multicylinder pump for viscous liquids having a control valve unit on each cylinder consisting of two valves, an intake valve and discharge valve for each plunger piston. The plunger piston is acted upon by the hydraulic medium in a dual manner; one pressure and one intake valve from two of the cylinders are closed and then opened when the other two corresponding valves are closed.
In particular, this invention is applicable to two-cylinder piston pumps, which have the above mentioned four valves. Pumps installed according to this invention serve to pump thick liquids, which from time to time have different compositions. In addition to contaminated water, for example, water contaminated with various substances such as wood which collects from ships docking in Kiel, other solid contaminants such as mortar and concrete are discharged by pumps of this invention. The multicylinder piston-pump is guaranteed by its very construction to prevent any connection between the intake and compression stroke. In this way, a break in the circuit between the discharge outlet and discharge-medium inlet, such as in the case of a mortar and concrete discharge medium, will be replaced by a collection hopper inserted in the line.
2. Description of the Prior Art
It is known that in the multicylinder piston pumps, requirements such as those above, are fulfilled by valve seats. For this purpose, one employs a spherical or tapered valve head mounted on a rod, which by means of a hydraulic cylinder, can be moved so as to open or close the valve. One can select the dimensions so that the diameter of the valve seat is approximately four times the diameter of the rod. If, for example, the pumps are used for discharging a medium containing cement, difficulties will arise because the valves will lose their water-tightness. This can be attributed to the fact that the discharge medium will build up behind the head of the pressure valve and thus block the valve.
There are also pumps which have plunger piston valves having a tapered end. The deposit from the discharge medium is separated out during the return stroke of the piston. In this way, these valves have the advantage of remaining completely open so as to maintain a free cross-section of flow. There are still difficulties if one increases the shut-off cross-section by means of the plunger piston valve. Specifically in those cases, the pressure from the discharge medium which is exerted on the piston requires an enlargement in the size of the drive piston in the hydraulic cylinder. In turn, the volume of hydraulic medium necessary for the piston to move must also be greatly increased. As a result, there is an increase in the time-interruption during the pumping action of the piston. In addition, the back-up volume of the discharge medium increases when the valve is open and in turn leads to a further time-interruption in the pumping-cycle. This discontinuity of the discharge flow has a damaging effect on the pump's operation. If on the other hand, a large cross-section of flow were provided for the discharge mass a more continuous flow would result.
The invention poses the following task: to construct a plunger-piston for the multicylinder pump in such a way so that the front edge of the piston which is acted upon by the pressure of the discharge medium will comprise only a portion of the entire piston head. Also, the necessary dimensions of the intake cylinder should correspondingly be reduced so as to allow for the motion of the piston.